Chemistry A-Level OxfordAQA
Definitions Questions and Answers
First ionisation energy - answerThe energy required to remove one electron from each
atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions
Relative atomic/molecular mass - answerThe mean mass of an atom/compound of an
element, divided by 1/12th of the mass of an atom of carbon-12
Empirical formula - answerThe simplest whole number ratio of atoms of each element in
a compound
Molecular formula - answerThe actual number of atoms of each element in a compound
Electronegativity - answerThe ability of an atom to attract a pair of electrons towards
itself in a covalent bond
Enthalpy change - answerEnergy change at constant pressure
Standard enthalpy of combustion - answerEnthalpy change when 1 mole of a species i
completely burned in oxygen in constant pressure
Standard enthalpy of formation - answerEnthalpy change when 1 mole of a compound
is formed from its constituent elements
Hess' law - answerIf a reaction can take place by more than one route and the initial
and final conditions are the same, the total enthalpy change is the same regardless of
the route taken
Mean bond enthalpy - answerAn average over different compounds of the energy
required to break a bond
Redox - answerOxidation and reduction happening simultaneously
Activation energy - answerMinimum energy required for a successful collision to take
place
Rate of reaction - answerChange in concentration of a substance in a given time
Catalyst - answerSubstance that speeds up the reaction but is not used up
How catalysts work - answerProvide an alternative pathway with a lower activation
energy
Definitions Questions and Answers
First ionisation energy - answerThe energy required to remove one electron from each
atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions
Relative atomic/molecular mass - answerThe mean mass of an atom/compound of an
element, divided by 1/12th of the mass of an atom of carbon-12
Empirical formula - answerThe simplest whole number ratio of atoms of each element in
a compound
Molecular formula - answerThe actual number of atoms of each element in a compound
Electronegativity - answerThe ability of an atom to attract a pair of electrons towards
itself in a covalent bond
Enthalpy change - answerEnergy change at constant pressure
Standard enthalpy of combustion - answerEnthalpy change when 1 mole of a species i
completely burned in oxygen in constant pressure
Standard enthalpy of formation - answerEnthalpy change when 1 mole of a compound
is formed from its constituent elements
Hess' law - answerIf a reaction can take place by more than one route and the initial
and final conditions are the same, the total enthalpy change is the same regardless of
the route taken
Mean bond enthalpy - answerAn average over different compounds of the energy
required to break a bond
Redox - answerOxidation and reduction happening simultaneously
Activation energy - answerMinimum energy required for a successful collision to take
place
Rate of reaction - answerChange in concentration of a substance in a given time
Catalyst - answerSubstance that speeds up the reaction but is not used up
How catalysts work - answerProvide an alternative pathway with a lower activation
energy
